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Author Topic: Shure Ksm32 - condenser capsule  (Read 5036 times)

radiovinhet

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Shure Ksm32 - condenser capsule
« on: October 24, 2016, 02:52:27 pm »

Hello!

How to get a k67 capsule,  working on Shure KSM 32... the original capsule was damaged... and i a have this k67 capsule that can be used on this mic, but KSM uses a pre-polarized capsule, not a real condenser, don't have any voltage to polarize the k67. There's a way to this work?

Best regards from Brazil
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Kai

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Re: Shure Ksm32 - condenser capsule
« Reply #1 on: October 24, 2016, 07:44:00 pm »

A simple solution would use the phantom power directly, like in the KM8x and early versions of the U87.
Have a look at their schemantics.
The sound would be somewhat softer, cause you end up with about 40 V instead of the 60(?) of the original.
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Timjag

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Re: Shure Ksm32 - condenser capsule
« Reply #2 on: October 24, 2016, 08:13:47 pm »

40volts is fine, but those Shures have crappy preamps any gain in sound from a nice capsule would be wiped out by the awful grainy pre-amp - you might as well build a new preamp in it, a nice little jfet mic like the old 414 or u87 preamp not stunning but very usable.

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radiovinhet

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Re: Shure Ksm32 - condenser capsule
« Reply #3 on: October 25, 2016, 09:39:57 am »

A simple solution would use the phantom power directly, like in the KM8x and early versions of the U87.
Have a look at their schemantics.
The sound would be somewhat softer, cause you end up with about 40 V instead of the 60(?) of the original.
Thanks, i'll try... 
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Kai

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Re: Shure Ksm32 - condenser capsule
« Reply #4 on: October 25, 2016, 10:30:25 am »

...crappy preamps any gain in sound from a nice capsule would be wiped out...build a new preamp in it
I would give it a try, you got the mic and the capsule - nothing to loose here.
All you need are two resistors about 10M (both the same, but exact size doesn't matter, I suggest 5-22M) taking phantom power from both pin 2+3.
At their joint a little foil cap 0.5uf/63V, one side to ground, one to the backplate.
The diaphrag goes to the amp's input, and you're done.
This arrangement prevents the polarization voltage from reaching the amp's input, it's the most simplistic arrangement.
I couldn't find a KMS32 schematic (the only link I found seemed to be a fake), but this should work.
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radiovinhet

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Re: Shure Ksm32 - condenser capsule
« Reply #5 on: October 25, 2016, 02:24:19 pm »

WOW! Thanks a lot, i'll try... nothing to loose  ;D
If works, i'll will post the results here. I have a k103 and c12 nylon to test too!
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Timjag

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Re: Shure Ksm32 - condenser capsule
« Reply #6 on: October 25, 2016, 05:29:49 pm »

Email shure for the schematic - they've always been really helpful, they have the attitude of devoting customer relationships over decades. I might have a contact. I'll have a look
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Michael O.

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Re: Shure Ksm32 - condenser capsule
« Reply #7 on: October 26, 2016, 12:58:16 am »

All you need are two resistors about 10M (both the same, but exact size doesn't matter, I suggest 5-22M) taking phantom power from both pin 2+3.
At their joint a little foil cap 0.5uf/63V, one side to ground, one to the backplate.
The diaphrag goes to the amp's input, and you're done.
This arrangement prevents the polarization voltage from reaching the amp's input, it's the most simplistic arrangement.

Cool, could this sort of simple circuit could be used in other electret mics that have had their not-so-permanently polarized electret capsules replaced with externally polarized condenser capsules? I have some old electrets lying around that are losing charge but have otherwise perfectly serviceable amplifier circuits. Also, pardon my inexperience, but 10M = 10 megohms, right?

Kai

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Re: Shure Ksm32 - condenser capsule
« Reply #8 on: October 26, 2016, 05:51:06 am »

Cool, could this sort of simple circuit could be used in other electret mics ....10M = 10 megohms, right?
10M means 10 MegaOhms.
Depends on the type of elektret capsule that is used.
Most cheap electret microphones have the amplifier (mostly just one FET transistor with one or two resistors) built into the capsule. If you remove it there is no amplifier left or an important part is missing.
What I have done: 
Open up the capsule and take out the amplifier to further use it.
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radiovinhet

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Re: Shure Ksm32 - condenser capsule
« Reply #9 on: October 27, 2016, 07:19:17 am »

Email shure for the schematic - they've always been really helpful, they have the attitude of devoting customer relationships over decades. I might have a contact. I'll have a look
I'm trying, but no success... i need to know the valeu for C11 cap on PCB, Shure don't sent it.

I've attached an akg ck12 nylon capsule to test, feed 48v on backplate, works!!!
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Kai

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Re: Shure Ksm32 - condenser capsule
« Reply #10 on: October 27, 2016, 08:11:37 am »

i need to know the valeu for C11 cap on PCB
Why specially this cap?
You could use a cap meter.

But- if it works mount the capsule and enjoy your new microphone  😊
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radiovinhet

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Re: Shure Ksm32 - condenser capsule
« Reply #11 on: October 27, 2016, 08:20:40 am »

Why specially this cap?
You could use a cap meter.

But- if it works mount the capsule and enjoy your new microphone  😊

The ex-owner gave me this defective ksm 32,  capsule was dead... then i replace it with a real condenser, now it's works. But the electronics is all SMD (and i don't know too much about electronics), and the capacitor named c11 on PCB  was replaced by a normal size  50v 1uF capacitor.. this is the only mod that i found and was replaced, sure. I need to know the original value... the mic has as 60Hz hum noise.
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Kai

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Re: Shure Ksm32 - condenser capsule
« Reply #12 on: October 27, 2016, 11:29:14 am »

...the mic has as 60Hz hum noise.
A 60Hz hum has more than likely nothing to do with internal parts modifications.
No 60Hz is present inside a correctly shielded housing. Check all metal parts and the PC-Board GND if they are properly connected to XLR pin 1.

Check your P48 supply:
Short XLR pin 1+3 with a short piece of wire directly at the preamps input connector (unbalance it). Now you can hear the noise of the unbalanced P48 feed by amplifying it with the preamp. No hum should be audible with reasonable gain settings.
It would be ideal if there is no difference in the residual noise if P48 is switched on or off. Practicality the results are better because the balancing cancels out about 30 to 60 dB of noise and hum.
But still, if exists, P48 hum could creep into the microphone, specially if something is wrong with its output stage.
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radiovinhet

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Re: Shure Ksm32 - condenser capsule
« Reply #13 on: October 27, 2016, 12:16:07 pm »

A 60Hz hum has more than likely nothing to do with internal parts modifications.
No 60Hz is present inside a correctly shielded housing. Check all metal parts and the PC-Board GND if they are properly connected to XLR pin 1.

Check your P48 supply:
Short XLR pin 1+3 with a short piece of wire directly at the preamps input connector (unbalance it). Now you can hear the noise of the unbalanced P48 feed by amplifying it with the preamp. No hum should be audible with reasonable gain settings.
It would be ideal if there is no difference in the residual noise if P48 is switched on or off. Practicality the results are better because the balancing cancels out about 30 to 60 dB of noise and hum.
But still, if exists, P48 hum could creep into the microphone, specially if something is wrong with its output stage.
I made some tests, i've changed the capacitor to another with 470uf, the hum/noise from amp it's gone... but ck12 nylon don't sounded too good, it haven't  much bass, the trebles are good...
i'll try the k67 or k103 from Neumann.

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mbrebes

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Re: Shure Ksm32 - condenser capsule
« Reply #14 on: October 27, 2016, 03:19:14 pm »

Don't forget that Shure will replace the KSM32 for a flat fee of $96, at least here in the US.
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